3.Theories of Organic Chemistry by Ferdinand August Karl Henrich (1922)"CHAPTER XVII THE theory of indicators AT the time of the development of the ionic
theory Ostwald l undertook an investigation in regard to the color of ions ..."

4.The Determination of Hydrogen Ions: An Elementary Treatise on the Hydrogen by William Mansfield Clark (1920)"... tration and which Noyes had previously summarized in his paper "Quantitative
application of the theory of indicators to volumetric analysis," (1910). ..."

5.Analytical Chemistry by Frederick Pearson Treadwell (1921)"Theory of Indicators* To detect the presence of free hydrogen cations or of
hydroxyl anions, certain colored, organic substances are used, called indicators ..."

7.Theories of Organic Chemistry by Ferdinand August Karl Henrich (1922)"CHAPTER XVII THE theory of indicators AT the time of the development of the ionic
theory Ostwald l undertook an investigation in regard to the color of ions ..."

8.The Determination of Hydrogen Ions: An Elementary Treatise on the Hydrogen by William Mansfield Clark (1920)"... tration and which Noyes had previously summarized in his paper "Quantitative
application of the theory of indicators to volumetric analysis," (1910). ..."